WeakReference

Class Overview

Implements a weak reference, which is the middle of the three types of references. Once the garbage collector decides that an object obj is is weakly-reachable, the following happens:

• A set ref of references is determined. ref contains the following elements:
  • All weak references pointing to obj.
  • All weak references pointing to objects from which obj is either strongly or softly reachable.
• All references in ref are atomically cleared.
• All objects formerly being referenced by ref become eligible for finalization.
• At some future point, all references in ref will be enqueued with their corresponding reference queues, if any.

Weak references are useful for mappings that should have their entries removed automatically once they are not referenced any more (from outside). The difference between a SoftReference and a WeakReference is the point of time at which the decision is made to clear and enqueue the reference:

• A SoftReference should be cleared and enqueued as late as possible, that is, in case the VM is in danger of running out of memory.
• A WeakReference may be cleared and enqueued as soon as is known to be weakly-referenced.

Summary

Public Constructors
	WeakReference(T r) Constructs a new weak reference to the given referent.
	WeakReference(T r, ReferenceQueue<? super T> q) Constructs a new weak reference to the given referent.

[Expand] Inherited Methods
From class java.lang.ref.Reference void clear() Makes the referent null. boolean enqueue() Forces the reference object to be enqueued if it has been associated with a queue. T get() Returns the referent of the reference object. boolean isEnqueued() Checks whether the reference object has been enqueued.
From class java.lang.Object Object clone() Creates and returns a copy of this Object. boolean equals( Object o) Compares this instance with the specified object and indicates if they are equal. void finalize() Invoked when the garbage collector has detected that this instance is no longer reachable. final Class<?> getClass() Returns the unique instance of Class that represents this object's class. int hashCode() Returns an integer hash code for this object. final void notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. final void notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. String toString() Returns a string containing a concise, human-readable description of this object. final void wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object. final void wait(long millis, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires. final void wait(long millis) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.